Chopper for electrical circuits



Ailg- 23, 1949 E. R. HABERLAND 2,479,566

CHOPPER FOR ELECTRICAL CIRCUITS I Filed July 13, 1945 2 Sheets-Sheet 1 Qwuam/Lo.

E.R.HABERLAND Patented Aug. 23, 1949 UNITED STATES PATENT OFFICE 2,479,536 CHOPPER FOR ELECTRICAL CIRCUITS Ernest R. Haber-lend, Washington, D. C. Application July 13, 1945, Serial No. 604,946 2 Claims. (Cl. 200-90) (Granted under the act of amended April 30, 1928;

This invention relates to a new and improved chopper for use in electrical circuits for converting low frequency currents into electrical impulses of higher frequency. The term chopper. as used herein, refers to any type of electrically driven circuit interrupter suitable tor use in detectlon circuits having means therein adapted to generate low frequency, low amplitude voltages.

corresponding to the aforesaid low frequency currents.

More specifically this invention relates to for preventing electrical leakage between the input and output circuits of such a chopper.

The chopper of the present invention is well suited, although obviously not limited, to use the detecting circuit disclosed in the (co-pending application of Haberland et al., for Electronic fiuxmeter and A. C. amplifier, Serial No. 824,620, died October 25, 194.5, this circuit being used pri marily for detecting the presence of :lerro mas acetic masses, depth charges, mines, ships, and torpedoes submerged in the water.

it is an object of the present invention to pro e a chopper that will have minimum current leakage between the driver coil the chopper contact circuit.

Another object is to provide a new and im proved detection circuit in which spurious leakage voltages of high frequency originating from the chopper driving source are prevented from small voltages of relatively low frecuency and amplitude generated by a high impedance detector.

it is a further object of the present invention to provide an improved mounting means for the terminals of the driver coil circuit in a chopper,

so that the latter are spaced as far as possible from the terminals of the chopping circuit consistent with the physical dimensions of the device.

An additional object is to arrange the chopper and driver coil terminals in widely spaced relation and to provide a rigid mounting for the coil terminals independently of the casing for the chopper whereby the casing may be removed without disconnecting the coil leads from the terminals therefor.

Still other objects, advantages and improvements will be apparent from the following description, taken in connection with the accompanying drawings, in which:

Fig. 1 shows a vessel In, such as a trawler, moving through the water and drawing a detecting device H, by cables l2l3; a mine I! rests on the bottom of the body of water.

Fig. 2 shows a circuit comprising two identical ill March 3, 1883, as 370 0. G. '35?) 2 gradiometer coils D--l and Ii -2, a filter circuit RC-l, the chopper OR, a coupling circuit RG-Z, a band pass amplifier AP, and a recorder R0.

Fig. 3 is a view in end elevation of the chopper, the casing being shown in section to expose the internal parts;

Fig. 4 is a view similar to Fig. 3 but showing the reverse side of the chopper, the casing again belog shown in section; and

Fig. 5 shows a top plan view of the chopper with the casing cut away to expose the internal parts.

Referring now to the drawings, and more par ticularly to Fig. 1, it will be seen that the detecting device l i is connected to the vessel in by a supporting cable and a transmission cable it. The detecting device comprises two enlarged end caps M and i6 composed of non-magnetic material and rigidly supported at either end of an elongated hub id in mutually parallel spaced relation. The end cap i l encloses the gradlometer coil Di and the end cap 5 E5 the gradiometer coll One conductor of the transmission cable 515; is connected to the gradiometer coil D-l and the other conductor to the gr-adiometer coil lie-2;

the two cells are connected in series opposition by a conductor 58 (Fig. 2) which passes through the elongated hub id. The gradlometer coils S -l and D-2 comprise the same number of turns of wire and are connected such that they are in inductive opposition to each other, as indicated by the arrows on Fig. 2, and thus the detecting device ii is unresponsive to angular motion of the device relative to the undistorted terrestrial magnetic field. The elongated hub it, which mounts the end caps it and I 6 and thus physically separates the gradiometer coils Dl and 13-2, is made of some suitable dlamagnetic material, preferably brass.

It is well known that a steel vessel has an inherent magnetic field of its own. The same is true of depth charges, mines, or torpedoes, which latter after spending their propelling force without exploding will sink to the bottom of the body of water. In any event, a vessel, depth charge, mine or torpedo resting on the bed of the body of water will, in addition to having its own inherent magnetic field, distort the ambient magnetic field of the earth and thus it will readily be seen that the presence of such metallic masses on the bottom of the body of water can be detected by the use of some apparatus, responsive to slight abnormalities in the ambient magnetic field, such as the differentially wound gradiometer coils D--l and 30-2.

I terminates at the contact ill of One terminal of the gradiometer coil D-i is connected by a conductor It to one fixed contact Bi oi the chopper CR oi the present invention. A conductor 20 extends from one terminal of the gradiometer coil D-Z to one input terminal of the band pass amplifier AP; as previously stated, the adjacent terminals of the gradlometer coils D-l and 13-2 are connected together by a conductor l8 (Fig. 2). Choppers of the type used here are usually fed with current of. sixty (60) cycle frequency supplied from a generator (not shown) on the trawler. It is desirable that any sixty cycle impulses induced in the gradiometer coils D-l and D-2 be filtered from the output of these coils. For this purpose a resistancecapacity filter RC-l is provided. This filter cir= cuit consists of two resistors Rl and 13-2 in series in the conductor is, a capacitor C-i bridged by a conductor 2i between the conductor it, at the juncture of the resistors Re-i and R-d, and the conductor 20, and a second capacitor C-2 bridged by a conductor 22 between the con= ductor is, at the outer terminal of the resistor 3-2, and the conductor 2t. With a sixty cycle input to the chopper CR and values for the gradiometer coils D-l and D-Z of 300 to 400 henries each, values of 100,000 ohms for the resis== tors R-i and Rr-2 and micro-farads for the capacitors -H and 6-2 have been found satis factory.

The chopper CR will be further described in detail hereinafter. Briefly it consists of an input or exciter coil 6d, a resilient armature st, and two fixed contacts and 55, mounted one on either side of the armature. The input coil 68 is connected to a suitable source of alternating current at the desired frequency by conductors id-l0. As previously stated, the conductor ts from the gradiometer coil D-l and the filter circuit RG-l the chopper. The other contact 55 of the chopper is connected by a conductor 23 to the conductor 29 extending from the gradiometer coil D-2 and the filter circuit RC-l to one input terminal of the band pass amplifier AP. A ground connection 26 is placed on the conductor 26 at the Junction of the d The output terminals of the band pass amplifier AP are connected by conductors 3! to a recorder R0. This latter may comprise a micro-ammeter butit is preferably one of the well known com mercial recording devices which rules a graphic line on previously prepared cross-section paper passing through the recorder.

Referring now to Figs. 3, and 5 it will be seen that the chopper CR comprises a base disc $35, made of electrical insulation material such, for example, as one of the well known phenolic con densation products, which has formed thereon a shoulder In the chopper or" the present iiivention three pins til-3 5-3t extend through the base disc in tight fitting relationship therein. A cover it! comprises a casing enclosing the working parts of the chopper, this cover having an out= wardly extending bottom flange 3%; which is in close fitting relationship and electrical engage ment with the shoulder 33 on the peripheral me= tallic ring member 32 surrounding base disc 85.

The internal parts of the chopper CR are mounted on a plate 3t which has a toe flange dd secured to the base disc 85, as by screws ti and arranged in overlying electrical engagement with. ring member 32 as at 8%. Slightly above the base disc 85 there is mounted on the plate fit a pair of aligned angle brackets secured to the mounting plate 35 by screws 33. Screws with suitable nuts thereon extend through aligned holes in the outwardly extending flanges of the angle brackets did-d2. (It will be understood that the screws M are insulated from each other and from the mounting 39 by suitable insulating bushings which extend from the heads of the screws to the nuts thereon, these bushings not being shown on the drawing.) Positioned be= tween the outwardly extending flanges oi the angle brackets 52-62 and on the screws dd there is a plurality (four) of insulating washers Intermediate the second and third insulating 'washers d5-t5 the butt of the armature id is latter with the conductor 2d. The armature 6dis connected by a conductor 25 to the other input terminal of the band pass amplifier AP.

A resistance-capacity coupling circuit RC-Q is provided for connecting the chopper CR and the gradiometer coils D-5 and D-2 and filter circuit RC-i to the band pass amplifier AP. This circuit consists of a capacitor C-d inter= posed in the conductor 25 intermediate the arma= ture It of the chopper CR and the input terminal of the amplifier AP, a resistor R- i bridged by a conductor 26 across the conductor 2i, inter mediate the armature 46 and the capacitor (3-3, and the conductor 20, and a resistor R-fi bridged by a conductor 2: across the conductor 25, intermediate the capacitor 0-3 and the input terminal of the amplifier AP, and the conductor 2d.

Values of one-tenth micro-faradior the capacitor 0-3 and one megohm each for the resistors R3 and Rt have been found satisfactory.

The band pass amplifier AP is designed to pass a current of one frequency only, for instance sixty cycles. A battery BA-I is connected to the band AP by conductors 28 and 29 and supplies filament current for the vacuum tubes of the amplifier; likewise, a battery BA-2 is connected to the amplifier AP by conductors 2e and gilband supplies plate current for the vacuum u es.

pass amplifier butt of a second fixed spring contact member dd mounted on the screws lid and the insulating bushings carried thereby.

The armature dd is made of any suitable material having the requisite degree of resiliency and high magnetic permeability, preferably spring steel, for a purpose which will appear hereinafter. Attached to the armature (it in any suitable man ner on either side thereof and positioned slightly below the mid-section thereof, there is a pair of contacts illl composed preferably of plati= hum-iridium alloy. An integral connector lug 53 is formed on the butt of the armature 56 and a conductor 69 is attached to this connector lug and to the middle pin 35, extending through the base disc 32. Similarly, intermediate the first and second insulating washers 65- 55, and again on the insulating bushings carried by the screws id-d4, the butt of a. fixed spring contact mem ber 50 is mounted. This fixed spring contact member has a contact 5i secured thereto in any suitable manner, this contact being positioned about'two-thirds of the length from the bottom and in alignment with the contacts Iiii? carried by the armature ed. The contact 56 is also preferably made of platinum-iridium alloy. An integral connector lug 52 is formed on the butt of the fixed spring contact member 50 and a conductor '53 is attached to this connector lug and to the pin 3d extending through the base disc 85.

Likewise, intermediate the third and fourth insulating washers 45-45, and also on the insulating bushings carried by the screws A i-4d, the

tact member 54, thereby is mounted, this fixed spring contact member being positioned on the opposite side of the armature 46 from the first fixed spring contact member 60. The second fixed spring contact member 54 also has a contact 66 secured thereto in any suitable manner, this contact being likewise positioned about two-thirds of'the length from the bottom and in alignment with the contacts 41-41 mounted on the armature 46 and the contact 6| mounted on the opposite fixed spring contact member '50, when the armature 46 and the fixed spring contact members 50 and 64 are in assembled relationship, The contact 66, like the contacts 41-4! and is also preferably made of platinum-iridium alloy. As before, an integral connector lug 56 is formed on the butt of the fixed spring contact member 54 and a conductor 61 is attached to this connector lug and to the pin 36 extending through the base disc 86.

Mounted on the plate 39 above the aligned contacts 41--5l-55 and attached to this plate by screws 58 there is a pair of aligned bracket members 69-59, these being positioned on either side of the armature 46. Each of these bracket memhers is slotted longitudinally at 60 and a threaded hole is formed longitudinally through each bracket member on the center plane of the slot. Set screws 6I--6l are mounted in these holes in the bracket members 59-59, respectively, and these set screws are aligned with and abut the up per ends of the fixed spring contact members 56 and 54, respectively. The set screws 6l-6l func tion as adjustment means for determining the positions of the fixed spring contact members 56 and 54 and the contacts "5! and 55, respectively, carried thereby with respect to the contacts ll- 4'! carried by the intermediate armature #6. Locking screws 62-62 pass freely through suitable holes in the upper partially severed portions of the bracket members 5959 and are received in threaded continuations of these holes in the lower portions of these bracket members. Bracket members 5s e9 and screws 58 are arranged in electrical engagement with plate 39, and one of set screws cl is arranged in electrical engagement with bracket member 5a and spring conto connect the ring member 32, casing 31 and plate 39 to the ground ed terminal prong 36. Set screw ii, in engagement with spring contact member 50, however, is insulated therefrom in the usual manner.

Above the bracket members fit-59 a iii-shaped permanent magnet 63 is secured in flat relationship on the mounting plate 39 by screws 6464, this magnet preferably being made of the magnetic alloy known commercially as Ainico. The uppermost leg of the C-shaped permanent magnet 63 has the gap 65 therein. As best shown in Fig. 5, this gap is triangular in shape cross-wise oi the leg of the magnet adjacent the mounting plate 39 and this triangular portion merges into a rectangular portion adjacent to the outer face of the magnet. Obviously the magnetic flux lines will be concentrated in the rectangular portion of the air gap, that is the portion of the air gap of least reluctance. The armature 46 extends upwardly past the top-most leg of the C-shaped permanent magnet 63 and sweeps past the rectangular portion of the gap 65 in this leg during each vibrational swing thereof.

A coil 66 is preferably rectangular in cross-section and formed in square shape. This coil is secured to the mounting plate 39 by a bracket 61 which is held in place by the screws 6464 which also holds the C-shaped permanent magnet 63 or rest position along the to the mounting plate. The bracket 61 is generally U-shaped and the U-shaped legsof the bracket have integral lugs 68 bent at ninety degrees (90), these lugs holding the coil 66 in place. Also, the bracket 61 has outwardly extending toe flanges 69-68 through which the mounting screws 64-64 extend. In the assembled relationship, the armature 46 is positioned in its center vertical axis of the coil parallel to the sides of and bisecting the ends 66 and vibrates in a plane the coil, as shown in Fig. 3, of the coil.

It will be readily seen that if alternating current is passed through the coil 66, the free end of the armature 46 will be alternately magnetized and thus attracted and repelled alternately by the poles of the permanent magnet 63. By this arrangement the armature 46 oscillates at the frequency of the current through the coil 66.

Conductors l010 extend .from the exciter coil 66 through holes in the mounting plate 39.

In the chopper arrangements of the prior art the conductors Hi-l6 have been extended to two (2) additional pins, similar to the pins 34-35-36 in the base disc 85, and adjacent to these latter pins. However, moisture has been found to collect on the bottom of the base disc 85, thereby reducing the insulating resistance of same, and in the said devices of the prior art a potential of approximately three volts has been found to exist across the pins to which the conductors ill-76 were connected, that is across the resistor 3-3, as a result of this leakage potential between the pins. Since the output potential of the gradiometer coils D- l and 33-4 is only a few milli-volts, the existence of this leakage potential has been found to disrupt the operation of the apparatus. This disadvantage of the prior art devices is ohviated in the chopper of the instant invention by bringing the conductors ill-ill out through the top of the casing 31 and in this manner they are as widely separated as possible within the limits of the physical dimensions oi the device, from the pins 3-l-35-36 in the base disc to which the contact 5?, armature 36, and the contact {55, respectively, are connected. Also in the chopper of the present invention, the casing 3'! functions as a shielding-means between the conductors 76lll from the exciter coil 66 and the pins 34-35-416 in the base disc 85, this casing being grounded as aforesaid, to terminal prong 38 in the manner of the usual construction of such devices.

It is desired, in addition to ductors iii-79 out through the top of casing 31, as aforestated, that the terminals for the conductors be rigidly mounted on plate 39 whereby the casing may be removed from the chopper without requiring that the coil conductors be disconnected from the terminals therefor. Referring now to Fig. 4, it will be seen that a mounting structure is provided which satisfies this requirement. A terminal block ll of insulating material is secured on the reverse side of the mounting plate 39 by screws 72, this block being positioned slightly below the screws 64-454 which hold the C-shaped permanent magnet 63 in place on the other side of the mounting plate. Conductor rods 13-13 extend through the top of the casing 31 and are threaded at both their upper and lower ends, the lower ends passing freely through suitable holes in the insulating block ll. Nuts 14-14 are mounted in face-to-face relationship on the lower threaded ends of the conductor rods 1313 on the opposite sides of the insulating block H,

bringing the con a washer 15 being interposed between each nut 14 and the block. The conductors IO-Ill extending from the coil 86 are attached, respectively, to the washers 15-15 on the upper side of the insulating block ll, as by soldering. The conductor rods Ili -I3 extend through grommets HG-l8, respectively, mounted in suitable holes in the top oi the casing 37 and disc nuts llll are mounted on the conductor rods in abutting relatiop with these grommets. Knurled binding post nuts it-I6 mounted on the tops of the conductor rods 15-15 respectively, complete the assembly. Continuation conductors ls-I9 have their termi nals gripped between the disc nuts ll-ill and the binding post nuts it-4t respectively, and these conductors extend to the generator or other alternating power supply (not shown) for the coil db.

lf'he operation of the chopper of the present in== vention in connection with the circuit disclosed should be readily apparent from the preceding description of the circuit arrangement and structure of the chopper. It may, however, be briefly summarized as follows: The detecting device it is towed through the water by the vessel ill, the

chopper CR being continually excited from a suitable source of alternating current, preferably oi. sixty cycle frequency, on the detecting device ll traverses the earth's un= distorted magnetic field, which is quite unifo for a given area, the electro-motive forces in= duced in the difierentially wound gradiometer coils D-l and D-Z will be equal and will counterbalance each other and there will be no disturbance in either the filter circuit RC-l' or the the couplin circuit RC-2. However, should the detecting device ll pass in the vicinity of a sub= merged metallic mass, such as a depth charge, submarine, torpedo, or mine ill, as shown, the earth's field being distorted in this vicinity, would induct in the gradiometer coils D-l and D-2 electromotive forces of different strength and thus unbalance the inductive reactance of the coils.

The difierence in the electro-motive forces gen= erated in the gradlometer coils D-i and D--2 will cause a current to flow in the filter circuit RC-l which circuit, as previously stated, eliminates the stray currents induced in the gradiometer coils by the sixty cycle power supply for the chopper CE. The current resulting from the unbalanced electromotive forces in the gradiometer coils D-'-I and D-2 will rise slowly to a maximum as the detecting device H passes into the portion of the magnetic field of greatest distortion and then decay as the detecting device passes out of the distorted magnetic field into the normal earths field surrounding the instant area. However, for all practical purposes, this current may be considered a steady state current and such current would be of no use for operating a receiver, such as the recorder R0. The chopper CR breaks this current up into a pulsating electromotive force which is transmitted by the resistance-capacity coupling circuit RC2 to the band pass amplifier AP. The resistor Rr-3 and the ground connection 24 hold the potential of the armature 46 of the chopper CR. to ground when the armature engages contact 55 and no signal is being received from the gradiometer coils D-l and D2; the capacitor C-3 is a blocking capacitor for keeping any direct output potential of the chopper CR oil the grid of the first (not shown) in the band pass amplifier AP; and the resistor R-l operates as a grid leak for the the towing vessel. As

stage vacuum tube first stage vacuum tube in the amplifier. the band pass amplifier Al? selects a narrow ire uency band, in this case around cycles, converts this to direct current, integrates the direct current wave with respect to e, and transmits the integrated wave to the recorder R0 which records same.

The aicredescribed mounting of the driving coil and chopper contact teals in widely spaced and ely insulated relation at their respective points of emergence from the ill and base 82 substantially prevents leakage oi current from the driving source to the chopper contact terminals, which leakage otherwise would obscure the signal voltage appearing at the eon= tact tels. cover, by reason of tin grounding of the cg, the signal voltage and the driving coll voltage are both above ground potential, and it lege paths develop between the casing and the coil a chopper contact ter= minals, the signal and driving coil voltages each will cause leakage currents to flow to ground rather than between the tools.

Qapacitive coupling between the coil driving circuit and the signal circuit is present to some extent due to the relatively high frequency the coil driving current. Leakage of current into the signal circuit and resultant distortion of the sig= nal due to this coupling. however, is substantially reduced in the interrupter switch arrangement or the present invention by reason oil the wide spac= ing between the signal and coil driving terminals 36-35-36 and lid respectively, at the points or connection into their respective chcuits out= side the casing Bl. Wide spacing of the tenals greatly decreases the'value of the stray capacitance between the signal and coil circuits and thus substantially reduces the capacitive coupling therebetween, and the casing fil and plate 39 by reason of their grounded connection, as aforedescribed, additionally serve to shield the enclosed signal circuit elements from the efiects oi capacitive coupling with the coil driving cir cult.

While there is shown and described herein a certain preferred embent oi the invention, many other and varied forms and uses will present themselves to those versed in the art without departing from the spirit of the inventionand the invention, therefore, is not limited the: in struc ture or in use except as indicated the terms and scope of the appended claims.

The invention herein described and claimed may be manufactured and used or for the Government of the United States of America for governmental purposes without the payment or any royalties thereon or therefor.

What is claimed as new and desired to be socured by Letters Patent of the United States is:

l. A vibratory signal circuit interrupter for converting signals of low frequency and low po= tential in the circuit to relatively high frequency pulses without distorting the signal comprising, in combination, a base formed of electrical insu lation material, a metallic member surrounding the-periphery of said base, a metallic casing removably mounted on said base in electrical engagement with said member and having a pair of openings arranged therein in maximum spaced relation with respect is mounted thereon, a metallic plate secured at right angles to said base in electrical engagement with said member and enclosed by said casing, a strip. of electrical insulation material secured to one side of said plate in widely spaced parallel to said base when the casing 1 between.

posts from said casing, a pair of terminal means high i'r 2. A signal circuit interrupter operable from a connecting the terminal posts to a relatively high interrupter contacts mounted on said plate, terstantially to prevent current leakage from said tively, said terminal prongs being extended outdriving coil circuit to said signal circuit due to minal prongs at their respective points of emercrease the capacitance or the capacitive paths Number therebetween, one of said terminal prongs be ng 1,578,707 electrically grounded in said circuit and the in- 1,583,792 rrupter contact connected thereto being 1,676,973 grounded to said plate whereby the plate and 1,680,667 casing are maintained at ground potential there- 1,943,240 by. to prevent electrical coupling between the 2, 86,848 ving coil circuit and said signal circuit sum- 2,288,449 cient to substantially e distortion of the 2,423,524

electrical coupling therebetween.

ERNEST. R.

REFERENCES CITED NITED STATES PATEN'IS Bide July 8, 1947 

